NBER WORKING PAPER SERIES INEQUALITY AT BIRTH: SOME CAUSES AND CONSEQUENCES Janet Currie Working Paper 16798 http://www.nber.org/papers/w16798 NATIONAL BUREAU OF ECONOMIC RESEARCH 1050 Massachusetts Avenue Cambridge, MA 02138 February 2011 I am grateful to W. Bentley MacLeod for his advice and support and to the MacArthur Foundation and the Center for Health and Well Being at Princeton University for supporting this research. Douglas Almond, and seminar participants at the German Economic Association meetings for 2010, the Harvard Kennedy School and the University of Chicago’s Harris School provided helpful comments on early drafts. Samantha Heep, Katherine Meckel, and David Munroe provided outstanding research assistance. The views expressed herein are those of the author and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peer- reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications. © 2011 by Janet Currie. All rights reserved. Short sections of text, not to exceed two paragraphs, may be quoted without explicit permission provided that full credit, including © notice, is given to the source. Inequality at Birth: Some Causes and Consequences Janet Currie NBER Working Paper No. 16798 February 2011 JEL No. I12,Q51,Q53 ABSTRACT Recent research shows that health at birth is affected by many factors, including maternal education, behaviors, and participation in social programs. In turn, endowments at birth are predictive of adult outcomes, and of the outcomes of future generations. Exposure to environmental pollution is one potential determinant of health at birth that has received increasing attention. A large literature outside of economics advocates for “Environmental Justice,” and argues that poor and minority families are disproportionately exposed to environmental hazards. I provide new evidence on this question, showing that children born to less educated and minority mothers are more likely to be exposed to pollution in utero and that white, college educated mothers are particularly responsive to changes in environmental amenities. I estimate that differences in exposure to toxic releases may explain 6% of the gap in incidence of low birth weight between infants of white college educated mothers and infants of black high school dropout mothers. Janet Currie International Affairs Building Department of Economics Columbia University - Mail code 3308 420 W 118th Street New York, NY 10027 and NBER [email protected] Economists have long been interested in the origins of inequality between individuals and between groups. Richard Ely, the founder of the American Economic Association and the person honored by these lectures, was certainly concerned about the “… share of the total product of industry that is received by each section of the community” (Richard T. Ely, Thomas S. Adams, Max O. Lorenz, Allyn A. Young, 1910, page 542). In his 1910 Outlines of Economics, he concluded the chapter on the personal distribution of wealth with a call to action: “Society must, therefore, take measures to better the environment of the poor. They must be taught to live wisely, and their children must be given a fair chance in life” (Ely, et al., 1910, page 550). In calling for reform, he explicitly rejected the view that poverty simply reflected the distribution of native abilities in the population and was therefore immutable. Today, the same debate is often framed in terms of “nature vs. nurture.” Endowments at birth are thought of as representing “nature” and differences in achievements between similarly endowed groups reflect “nurture”. In this lecture, I will explore the possibility that differences that are often thought to be innate, may in fact reflect the effects of “nurture” or interactions between “nature and nurture,” and like Ely, I will focus on the importance of giving children a fair chance in life. The first part of the lecture will review some of the evidence about the determinants of health at birth. I argue that individuals may start with very different endowments at birth because of events that happened to them during a critical period: The nine months that they were in utero. In turn, endowments at birth have been shown to be predictive of adult outcomes and of the outcomes of the next generation. This focus on the prenatal period suggests that differences that appear to be innate may in fact be the product of environmental factors. While summarizing several influences on health at 2 birth, I will give considerable attention to one particular example of an environmental influence: Prenatal exposure to pollution. A large literature outside of economics advocates for “Environmental Justice,” arguing that poor and minority families are disproportionately exposed to environmental hazards. But issues of data quality and weaknesses in methodology leave this assertion open to debate (William Bowen, 2002). I provide new evidence on this question, showing that children born to less educated and minority mothers are indeed more likely to be exposed to pollution in utero. The gradients in pollution exposure by maternal race and education are clear cut when we use data at a fine enough level of geographic disaggregation. More strikingly, I show that these gradients can arise quickly following changes in environmental conditions and that white, college educated mothers are particularly responsive to these changes. These results shed light on some of the mechanisms underlying the perpetuation of lower socioeconomic status. Poor and minority children are more likely to be in poor health at birth, partly because their mothers are less able to provide a healthy fetal environment. Poor health at birth is associated with poorer adult outcomes, which in turn provide less than optimal conditions for the children of the poor. This conclusion suggests that policy makers attempting to ameliorate inequalities among children cannot afford to ignore mothers, since what mothers do even before they know they are pregnant may have profound consequences. I. Endowments at Birth and Future Outcomes This section provides an overview of the literature on health at birth with the aim of establishing five important points: First, there are large and persistent inequalities in health at birth. Second, the persistence of disparities cannot be taken as evidence that the source of 3 disparities is “genetic.” Indeed, the sharp distinction that is often made between “nature and nurture” is now outdated and unhelpful. Third, health at birth is surprisingly malleable and reflects the influences of a wide range of individual and social factors. Fourth, health at birth is a useful predictor of important future outcomes such as earnings, education, and disability, though the long-term effects of health at birth are themselves amenable to environmental influences. Fifth, there is increasing evidence of intergenerational transmission of poor infant health at birth. a) Endowments at Birth, Genes, and the Epigenome Table 1 shows data calculated using singleton births from the U.S. National Individual- Level Natality Data.1 This database contains information about virtually all of the approximately 4 million births per year in the U.S. The table illustrates huge inequality in health at birth. For example, the incidence of low birth weight (birth weight less than 2500 grams) is more than three times higher among children of black high school dropout mothers than among children of white college educated mothers. Although this lecture will focus on low birth weight as the measure of health at birth, disparities are also present if we look at alternative indicators such as prematurity.2 I focus on birth weight because it has been measured over a long period of time and is widely available. Moreover, while the limitations of birth weight as a summary measure are increasingly well understood (see Douglas Almond, Kenneth Y. Chay, and David Lee, 2005), little progress has been made towards finding an alternative, superior measure. Thus, for the 1 I focus on singleton births because multiple births are much more likely to be low birth weight and many multiple births result from Assisted Reproductive Technologies (ART). If one looks at all births, the fraction low birth weight among white college educated mothers has increased more than Table 1 suggests, because these mothers are more likely than others to use ART. 2 Disparities are also seen in APGAR scores. The APGAR score is a rating from zero to ten of the infant’s health 5 minutes after birth. Wanchuan Lin (2008) shows that while there was no convergence in the incidence of low birth weight from 1983 to 2000, gaps in APGAR scores and infant mortality declined, largely due to improvements in medical care at the time of child birth. 4 time being we must look under the lamp-post, while hoping that a better light source will soon become available. Table 1 indicates that differences in endowments at birth have been relatively stable over time. There has been a tendency to view this stability as indicative of group-level genetic differences (Richard J. Herrnstein and Charles Murray, 1994). Yet the emerging science of epigenetics suggests that a much subtler interplay of genes and the environment is at work. Arturas Petronis (2010) argues that “it is difficult to visualize how highly stable DNA sequences can account for heritability which is malleable and context-dependent” (page 722). A puzzle brought to light by the sequencing of the human genome is that human beings have so few genes - approximately 23,000, about the same number as a fish or a mouse. It seems that there are too few genes to explain the complexity of humankind. Moreover, we now know that unrelated individuals share over 99% of their DNA and that those genetic variations (polymorphisms) that have been identified explain little of the variation observed in the population (Lars Feuk, Andrew R.